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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.axis2.jaxws.message.impl;

import org.apache.axiom.blob.Blobs;
import org.apache.axiom.om.OMDataSourceExt;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMException;
import org.apache.axiom.om.OMXMLBuilderFactory;
import org.apache.axiom.om.OMXMLParserWrapper;
import org.apache.axiom.om.ds.AbstractOMDataSource;
import org.apache.axiom.om.ds.BlobOMDataSource;
import org.apache.axiom.om.util.StAXUtils;
import org.apache.axis2.jaxws.ExceptionFactory;
import org.apache.axis2.jaxws.i18n.Messages;
import org.apache.axis2.jaxws.message.Block;
import org.apache.axis2.jaxws.message.Message;
import org.apache.axis2.jaxws.message.factory.BlockFactory;
import org.apache.axis2.jaxws.message.util.Reader2Writer;
import org.apache.axis2.jaxws.spi.Constants;
import org.apache.axis2.jaxws.utility.JavaUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import javax.xml.namespace.QName;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.XMLStreamWriter;
import javax.xml.ws.WebServiceException;
import java.io.StringReader;
import java.io.UnsupportedEncodingException;

/**
 * BlockImpl Abstract Base class for various Block Implementations.
 * 
 * The base class takes care of controlling the transformations between BusinessObject,
 * XMLStreamReader and SOAPElement A derived class must minimally define the following:
 * _getBOFromReader _getReaderFromBO _outputFromBO
 * 

 * In addtion, the derived class may want to override the following: _getBOFromBO ...if the
 * BusinessObject is consumed when read (i.e. it is an InputSource)
 * 
 * The derived classes don't have direct access to the instance data. This ensures that BlockImpl
 * controls the transformations.
 */
public abstract class BlockImpl extends AbstractOMDataSource implements Block {

    private static Log log = LogFactory.getLog(BlockImpl.class);

    protected T busObject;
    protected C busContext;

    protected OMElement omElement = null;

    protected QName qName;
    private boolean noQNameAvailable = false;
    
    protected BlockFactory factory;
    protected boolean consumed = false;
    protected Message parent;
    
    /**
     * A Block has the following components
     *
     * @param busObject
     * @param busContext or null
     * @param qName      or null if unknown
     * @param factory    that creates the Block
     */
    protected BlockImpl(T busObject, C busContext, QName qName, BlockFactory factory) {
        this.busObject = busObject;
        this.busContext = busContext;
        this.qName = qName;
        this.factory = factory;
    }

    /**
     * A Block has the following components
     *
     * @param reader
     * @param busContext or null
     * @param qName      or null if unknown
     * @param factory    that creates the Block
     */
    protected BlockImpl(OMElement omElement, C busContext, QName qName, BlockFactory factory) {
        this.omElement = omElement;
        this.busContext = busContext;
        this.qName = qName;
        this.factory = factory;
    }
    
    // Hack to disambiguate the constructors is T = OMElement
    protected BlockImpl(C busContext, OMElement omElement, QName qName, BlockFactory factory) {
        this(omElement, busContext, qName, factory);
    }

    /* (non-Javadoc)
      * @see org.apache.axis2.jaxws.message.Block#getBlockFactory()
      */
    @Override
    public final BlockFactory getBlockFactory() {
        return factory;
    }

    /* (non-Javadoc)
      * @see org.apache.axis2.jaxws.message.Block#getBusinessContext()
      */
    @Override
    public final Object getBusinessContext() {
        return busContext;
    }

    @Override
    public final Message getParent() {
        return parent;
    }

    @Override
    public void setParent(Message p) {
        parent = p;
    }

    /* (non-Javadoc)
      * @see org.apache.axis2.jaxws.message.Block#getBusinessObject(boolean)
      */
    @Override
    public final T getBusinessObject(boolean consume)
            throws XMLStreamException, WebServiceException {
        if (consumed) {
            throw ExceptionFactory.makeWebServiceException(
                    Messages.getMessage("BlockImplErr1", this.getClass().getName()));
        }
        if (busObject != null) {
            busObject = _getBOFromBO(busObject, busContext, consume);
        } else {
            // Transform reader into business object
            busObject = _getBOFromOM(omElement, busContext);
            omElement = null;
        }

        // Save the businessObject in a local variable
        // so that we can reset the Block if consume was indicated
        T newBusObject = busObject;
        setConsumed(consume);
        return newBusObject;
    }
    

    /* (non-Javadoc)
      * @see org.apache.axis2.jaxws.message.Block#getQName()
      */
    @Override
    public final QName getQName() throws WebServiceException {
        // If the QName is not known, find it
        try {
            if (qName == null) {
                // If a prior call discovered that this content has no QName, then return null
                if (noQNameAvailable) {
                    return null;
                }
                if (omElement == null) {
                    try {
                        XMLStreamReader newReader = _getReaderFromBO(busObject, busContext);
                        busObject = null;
                        OMXMLParserWrapper builder = OMXMLBuilderFactory.createStAXOMBuilder(newReader);
                        omElement = builder.getDocumentElement();
                        omElement.close(true);
                    } catch (Exception e) {
                        // Some blocks may represent non-element data
                        if (log.isDebugEnabled()) {
                            log.debug("Exception occurred while obtaining QName:" + e);
                        } 
                        if (!isElementData()) {
                            // If this block can hold non-element data, then accept
                            // the fact that there is no qname and continue
                            if (log.isDebugEnabled()) {
                                log.debug("The block does not contain an xml element. Processing continues.");
                            }
                            // Indicate that the content has no QName
                            // The exception is swallowed.
                            noQNameAvailable = true;
                            return null;
                        }  else {
                            // The content should contain xml.  
                            // Rethrowing the exception.
                            throw ExceptionFactory.makeWebServiceException(e);
                        }
                    }
                }
                qName = omElement.getQName();
            }
            return qName;
        } catch (Exception xse) {
            setConsumed(true);
            throw ExceptionFactory.makeWebServiceException(xse);
        }
    }

    /**
     * This method is intended for derived objects to set the qName
     *
     * @param qName
     */
    protected final void setQName(QName qName) {
        this.qName = qName;
    }

    /* (non-Javadoc)
      * @see org.apache.axis2.jaxws.message.Block#getXMLStreamReader(boolean)
      */
    @Override
    public final XMLStreamReader getXMLStreamReader(boolean consume)
            throws XMLStreamException, WebServiceException {
        XMLStreamReader newReader = null;
        if (consumed) {
            // In some scenarios, the message is written out after the service instance is invoked.
            // In these situations, it is preferable to simply ignore this block.
            if (this.getParent() != null && getParent().isPostPivot()) {
                return _postPivot_getXMLStreamReader();
            }
            throw ExceptionFactory.makeWebServiceException(
                    Messages.getMessage("BlockImplErr1", this.getClass().getName()));
        }
        if (omElement != null) {
            newReader = omElement.getXMLStreamReader(!consume);
            if (consume) {
                omElement = null;
            }
        } else if (busObject != null) {
            // Getting the reader does not destroy the BusinessObject
            busObject = _getBOFromBO(busObject, busContext, consume);
            newReader = _getReaderFromBO(busObject, busContext);
        }
        setConsumed(consume);
        return newReader;
    }

    /* (non-Javadoc)
      * @see org.apache.axiom.om.OMDataSource#getReader()
      */
    @Override
    public final XMLStreamReader getReader() throws XMLStreamException {
        return getXMLStreamReader(true);
    }

    /* (non-Javadoc)
      * @see org.apache.axiom.om.OMDataSource#serialize(javax.xml.stream.XMLStreamWriter)
      */
    @Override
    public final void serialize(XMLStreamWriter writer) throws XMLStreamException {
        outputTo(writer, isDestructiveWrite());
    }

    @Override
    public OMElement getOMElement() throws XMLStreamException, WebServiceException {
        OMElement newOMElement = null;
        boolean consume = true;  // get the OM consumes the message
        if (consumed) {
            throw ExceptionFactory.makeWebServiceException(
                    Messages.getMessage("BlockImplErr1", this.getClass().getName()));
        }
        if (omElement != null) {
            newOMElement = omElement;
        } else if (busObject != null) {
            // Getting the reader does not destroy the BusinessObject
            busObject = _getBOFromBO(busObject, busContext, consume);
            newOMElement = _getOMFromBO(busObject, busContext);
        }
        setConsumed(consume);
        return newOMElement;
    }
    

    /* (non-Javadoc)
      * @see org.apache.axis2.jaxws.message.Block#isConsumed()
      */
    @Override
    public final boolean isConsumed() {
        return consumed;
    }

    /**
     * Once consumed, all instance data objects are nullified to prevent subsequent access
     *
     * @param consume
     * @return
     */
    public final void setConsumed(boolean consume) {
        if (consume) {
            this.consumed = true;
            busObject = null;
            busContext = null;
            omElement = null;
            if (log.isDebugEnabled()) {
                // The following stack trace consumes indicates where the message is consumed
                log.debug("Message Block Monitor: Action=Consumed");
                log.trace(JavaUtils.stackToString());
            }
        } else {
            consumed = false;
        }
    }

    @Override
    public final boolean isQNameAvailable() {
        return (qName != null);
    }

    @Override
    public final void outputTo(XMLStreamWriter writer, boolean consume)
            throws XMLStreamException, WebServiceException {
        if (log.isDebugEnabled()) {
            log.debug("Start outputTo");
        }
        if (consumed) {
            // In some scenarios, the message is written out after the service instance is invoked.
            // In these situations, it is preferable to simply ignore this block.
            if (this.getParent() != null && getParent().isPostPivot()) {
                _postPivot_outputTo(writer);
            }
            throw ExceptionFactory.makeWebServiceException(
                    Messages.getMessage("BlockImplErr1", this.getClass().getName()));
        }
        if (omElement != null) {
            _outputFromOM(omElement, writer, consume);
        } else if (busObject != null) {
            if (log.isDebugEnabled()) {
                log.debug("Write business object");
            }
            busObject = _getBOFromBO(busObject, busContext, consume);
            _outputFromBO(busObject, busContext, writer);
        }
        setConsumed(consume);
        if (log.isDebugEnabled()) {
            log.debug("End outputTo");
        }
        return;
    }

    /**
     * Called if we have passed the pivot point but someone wants to output the block. The actual
     * block implementation may choose to override this setting
     */
    protected final void _postPivot_outputTo(XMLStreamWriter writer)
            throws XMLStreamException, WebServiceException {
        if (log.isDebugEnabled()) {
            QName theQName = isQNameAvailable() ? getQName() : new QName("unknown");
            log.debug("The Block for " + theQName +
                    " is already consumed and therefore it is not written.");
            log.debug("If you need this block preserved, please set the " + Constants
                    .SAVE_REQUEST_MSG + " property on the MessageContext.");
        }
        return;
    }

    /**
     * Called if we have passed the pivot point but someone wants to output the block. The actual
     * block implementation may choose to override this setting.
     */
    protected final XMLStreamReader _postPivot_getXMLStreamReader()
            throws XMLStreamException, WebServiceException {
        if (log.isDebugEnabled()) {
            QName theQName = isQNameAvailable() ? getQName() : new QName("unknown");
            log.debug("The Block for " + theQName +
                    " is already consumed and therefore it is only partially read.");
            log.debug("If you need this block preserved, please set the " + Constants
                    .SAVE_REQUEST_MSG + " property on the MessageContext.");
        }
        QName qName = getQName();
        String text = "";
        if (qName.getNamespaceURI().length() > 0) {
            text = "";
        } else {
            text = "<" + qName.getLocalPart() + "/>";
        }
        StringReader sr = new StringReader(text);
        return StAXUtils.createXMLStreamReader(sr);
    }

    /**
     * @return true if the representation of the block is currently a business object. Derived classes
     *         may use this information to get information in a performant way.
     */
    protected final boolean isBusinessObject() {
        return busObject != null;
    }

    @Override
    public final String traceString(String indent) {
        // TODO add trace string
        return null;
    }

    /**
     * The default implementation is to return the business object. A derived block may want to
     * override this class if the business object is consumed when read (thus the dervived block may
     * want to make a buffered copy) (An example use case for overriding this method is the
     * businessObject is an InputSource)
     *
     * @param busObject
     * @param busContext
     * @param consume
     * @return
     */
    protected T _getBOFromBO(T busObject, C busContext, boolean consume) {
        return busObject;
    }

    /**
     * Default method for getting business object from OM.
     * Derived classes may override this method to get the business object from a
     * data source.
     * 
     * @param om
     * @param busContext
     * @return Business Object
     * @throws XMLStreamException
     * @throws WebServiceException
     */
    protected abstract T _getBOFromOM(OMElement omElement, C busContext)
            throws XMLStreamException, WebServiceException;
    
    /**
     * Get an XMLStreamReader for the BusinessObject The derived Block must implement this method
     *
     * @param busObj
     * @param busContext
     * @return
     */
    protected abstract XMLStreamReader _getReaderFromBO(T busObj, C busContext)
            throws XMLStreamException, WebServiceException;
    
    /**
     * @param busObject
     * @param busContext
     * @return OMElement
     * @throws XMLStreamException
     * @throws WebServiceException
     */
    protected OMElement _getOMFromBO(T busObject, C busContext)
        throws XMLStreamException, WebServiceException {
        // Getting the reader does not destroy the BusinessObject
        XMLStreamReader newReader = _getReaderFromBO(busObject, busContext);
        OMXMLParserWrapper builder = OMXMLBuilderFactory.createStAXOMBuilder(newReader);
        return builder.getDocumentElement();
    }

    /**
     * Output Reader contents to a Writer. The default implementation is probably sufficient for most
     * derived classes.
     *
     * @param reader
     * @param writer
     * @throws XMLStreamException
     */
    protected final void _outputFromReader(XMLStreamReader reader, XMLStreamWriter writer)
            throws XMLStreamException {
        Reader2Writer r2w = new Reader2Writer(reader);
        r2w.outputTo(writer);
    }
    
    /**
     * Output OMElement contents to a Writer. The default implementation is probably sufficient for most
     * derived classes.
     *
     * @param om
     * @param writer
     * @throws XMLStreamException
     */
    protected final void _outputFromOM(OMElement omElement, XMLStreamWriter writer, boolean consume)
            throws XMLStreamException {
        if (consume) {
            if (log.isDebugEnabled()) {
                log.debug("Write using OMElement.serializeAndConsume");
            }
            omElement.serializeAndConsume(writer);
        } else {
            if (log.isDebugEnabled()) {
                log.debug("Write Using OMElement.serialize");
            }
            omElement.serialize(writer);
        }
    }
    
    /* (non-Javadoc)
     * @see org.apache.axiom.om.OMDataSourceExt#copy()
     */
    @Override
    public OMDataSourceExt copy() throws OMException {
        // TODO: This is a default implementation.  Much
        // more refactoring needs to occur to account for attachments.
        try {
            String encoding = "utf-8"; // Choose a common encoding
            byte[] bytes = this.getXMLBytes(encoding);
            return new BlobOMDataSource(Blobs.createBlob(bytes), encoding);
        } catch (UnsupportedEncodingException e) {
            throw new OMException(e);
        }
    }

    /**
     * Output BusinessObject contents to a Writer.
     * Derived classes must provide this implementation
     * @param busObject
     * @param busContext
     * @param writer
     * @throws XMLStreamException
     * @throws WebServiceException
     */
    protected abstract void _outputFromBO(T busObject, C busContext,
                                          XMLStreamWriter writer)
            throws XMLStreamException, WebServiceException;
}